A month prior, she had been found in snake-infested bushland in western Sydney with burns to 80 per cent of her body, the result of an acid attack.

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Four and a half years later, detectives are no closer to solving the killing that her 19-year-old son Daniel called "brutal" during a press conference appealing for information.

"Every person in our family was left traumatised; we were left scared and want answers," he told reporters in Sydney on Monday.

Monika Chetty was found with burns to 80 per cent of her body.

"As we keep growing older and older, we still don't have a mother. It's traumatising, it's painful. We just need answers," he said.

Ms Chetty had left her second husband Ronald in 2009. After a brief stint living with their mother, the couple's three children stayed with him.

Daniel Chetty said the family want answers over his mother's death. Credit:AAP

She drifted across western Sydney, living in small apartments, with friends and well-meaning acquaintances and eventually wound up living in her car and begging for money at shopping centres.

On January 3, 2014, two police officers found her in bushland with extensive burns from which she died.

Detectives spoke to her in the hospital, where she told them a man she had refused to give a cigarette threw "a substantial amount" of acid at her in Liverpool's Bigge Park, Detective Chief Inspector Sean Johnstone said on Monday.

The bushland location at West Hoxton where Monika Chetty spent a lot of time in her final weeks. Credit:Wolter Peeters

But forensic evidence has ruled the park out as a crime scene location, leading investigators to believe that she knew her attacker and was lying to protect herself or her family.

Monika Chetty died in the burns unit of Concord Hospital in January 2014.

Evidence shows Ms Chetty had been attacked between five and 10 days before she was taken to Concord Hospital.

"She must have been in a tremendous amount of pain and a tremendous amount of fear not to come forward to the authorities, and we want to know why," Chief Inspector Johnstone said.

Police are now looking at a number of lines of inquiry, including her potential involvement in a marriage visa scam.

They are also looking at suggestions this was not the first time she had been the victim of an acid attack, and are trying to understand why she refused all help from people she knew - aside from accepting money.